Thermographic copying apparatus with means to reverse the movement of a continuous transfer sheet



D 25, 1967 R. B. RUSSELL ETAL 3,316,403

THERMOGRAPHIC COPYING APPARATUS WITH MEANS TO REVERSE THE MOVEMENT OF A CONTINUOUS TRANSFER SHEET Filed Oct. 26, 1964 $52 FIG! (TD) R2 20 l RI I i I I I I I I 2| )QI Ii I Rl'2 I. Rz-z I I 'FH R3-I :1 FIGZ 1" f 53 A I I I INVENTORS I ROBERT B. RUSSELL *f k m GERARD A. VITU N U4 R|-| I8 M (me #%Q ArmR/wsys United States Patent Office 3,316,403 Patented Apr. 25, 1967 3,316,403 THERMOGRAPHIC COPYING APPARATUS WITH MEANS T REVERSE THE MOVEMENT OF A CONTINUOUS TRANSFER SHEET Robert B. Russell, Newton, Mass., and Gerard A. Vltu, Evanston, Ill.; said Vitu assignor, by mesne assignments, to Robert B. Russet], Boston, Mass.

Filed Oct. 26, 1964, Ser. No. 406,319 4 Claims. (Cl. 250-65) This invention is an improved thermographic copying machine and process for radiant energy induced copying by front printing using a continuous transfer sheet contained Within the machine. More specifically, this invention is concerned with such a copying machine and process so designed and operated as to reduce the amount of transfer sheet consumed per copy by providing for automatic partial-rewind of the transfer sheet after each copy is produced.

US. Patent No. 3,048,695, in the name of one of the present inventors illustrates the type of thermographic copying machine with which this invention is concerned. This patent develops the principals upon which the thermographic copying machine operates and it will not be necessary to unduly redescribe here the basic elements of the machine. Succinctly, the machine operates by placing first the indicia-bearing original against a print roll over which is placed the copy sheet. Both sheets are held firmly against the print roll by a continuous transfer sheet which contains the transfer or imaging material such as a wax on its surface. The three superimposed sheets are then passed under a high intensity radiant energy source such as a lamp. This causes the imaging material to soften or melt in the areas corresponding to the images on the original with the imaging material then transferring to the copy sheet. The three sheets are thereafter separated with the continuous transfer sheet being passed to a take-up roll within the machine.

One of the problems associated with such a thermographic copying machine is that after the original, copy sheet and transfer sheet have passed the radiant energy source it is necessary for the transfer sheet to continue to advance past the printing station to a position where the copy sheet and original can be ejected from the machine. There is, therefore, some appreciable spacing between the end of one original and the front or leading edge of the next original which spacing causes some portion of the transfer sheet to go unused. In normal operation, it is not practical to introduce originals into the machine one after another with substantially no spacing between them.

In the present invention means are provided for causing the transfer sheet to return or rewind to some extent after each copy has been separated so that the amount of transfer sheet consumed per copy is decreased. The amount of return provided for will usually be at least equal to the distance between the leading and trailing edges of successive originals. It has been found, however, that even a greater return can be provided for. There is usually upper and lower margins on letters and some overlap of successive originals with respect to the transfer sheet can be practiced. In addition, with most typed sheets the lines of typing usually cover less than 50% of the surface area of the sheet so that by proper registration of the amount of return, overlap of the overall imaged areas can also be practiced if desired. Wax-bearing transfer sheets have been made that will print two or three times from the same area. Transfer of the wax from an imaged area is usually not complete on the first use, i.e., not all of the wax is removed. Thus, if the return of the transfer sheet causes a spot or area where some of the wax has been removed to coincide with an image on the original to be reproduced, printing will still occur. The amount of return of the transfer sheet can be set therefore so that the amount of transfer sheet used per copy is one-quarter to one-third of the average length of the originals passed through the machine. Usually, however, the amount of return will be in the range of 25 to 50% of the distance traveled by the transfer sheet from a starting position to its ending position after removal of the imaged copy sheet.

The transfer sheet during its return or rewind can have the imaging material redistributed as by burnishing or brushing to further reduce any effects of overlap of the originals on the transfer sheet.

The return of the transfer sheet after ejection of the copy can be accomplished by any one of several means. A simple mechanical arrangement is to place a springtensioned guide roll or backlash roll in contact with the transfer sheet between the supply roll and the printing station. When the machine is turned off the backlash roll is adapted to pull the transfer sheet up or away from the printing station, with there being means Working in conjunction with the backlash roll for releasing the tension on the transfer sheet created by the take-up roll and/ or transfer sheet drive roll. The distance the end of an original must travel from the printing station to the point of separation from the transfer sheet and ejection from the machine is known and the backlash roll is adjusted to return the transfer sheet at least this distance, or a greater distance if desired.

In another method, a reading device that measures the length of the original passing through the machine can be used. This device then can be used to reverse the drive mechanism of the machine for an appropriate length of time to secure the desired distance of return. Instead of measuring the length of the original, the degree of rotation of the print roll can be suitably observed.

The reversing of the driving means of the machine can be quite simple when it is desired to have the transfer sheet return only a distance approximately equal to the distance between the leading and trailing edges of successive originals.

In brief compass, this invention is an improvement of a thermographic copying process wherein a continuous transfer sheet is fed from a supply roll past a printing station, a copy sheet and indicia-bearing original are placed adjacent to the transfer sheet at said printing station, radiant energy is directed at said printing station to cause the copy sheet to be imaged by the transfer sheet according to the pattern of the indicia-bearing original, the transfer sheet is advanced with the copy sheet so imaged past the printing station, the imaged copy sheet is then removed and the process is thereafter repeated. The improvement of this invention is designed to decrease the amount of transfer sheet consumed per copy and coinprises reversing the movement of the transfer sheet past the printing station during the interval between the removal of the imaged copy sheet and the next printing action. The amount of reversal of the transfer sheet Will usually be at least equal to approximately the distance the transfer sheet must travel from the time the trailing edge of the original passes the printing station to the time the original and imaged copy sheet are ejected from the machine, and usually the reversal will be no greater than that required to return the transfer sheet to its original starting position.

of this specification.

In the drawings:

FIG. 1 schematically illustrates one form of the thermographic copying apparatus of this invention. Two

3 different means for accomplishing reversal of the movement of the transfer sheet are shown in the single drawing but in actual practice only one such means would, of course, be used;

FIG. 2 illustrates an electric circuit for the apparatus of FIG. 1.

With reference to FIG. 1, the machine is contained in a housing 5 which has an entrance slot 6 for introducing the copy sheet and the indicia-bearing original and an exit slot 7 where they are ejected from the machine. The wax-coated transfer sheet 40 passes from supply roll 10 over guide roll 11 which firmly presses it against iprint roll 12. From there the transfer sheet travels past light source 13, around take-ofi roll 14, over guide roll and thence to the take-up or wind-up roll 16.

Pressing against the print roll 12 is a drive wheel 17 which forms a take-off nip with the print roll. As illustrated, drive wheel 17 is driven by motor 18 by means of a belt 8. Motor 18 through belt 9 going to pulley 31 also drives the takeup-roll 16. A belt 32 connects pulley 31 with pulley 33 on su ply roll 10. The relative sizes of pulleys 31 and 33 are such that take-up roll 16 turns at a slightly faster rate than supply roll 10. Behind pulley 31 is an electromagnetic actuated slip clutch 34. The slip clutch is adjusted to allow the desired amount of tension to be placed on the transfer sheet.

In operation, an indicia-bearing original with a superimposed copy sheet are introduced into the nip formed by the transfer sheet passing over roll 11 and roll 12 through entrance slot 6. The wax surface of the transfer sheet faces the copy sheet. The print roll is then rotated and carries the three sheets past light source 13 to takeoff roll 14. The sharp bending given the transfer sheet as it passes over roll 14 causes the imaged copy sheet and the original to separate and fall into the nip formed by roll 17 and roll 12. The two sheets are then passed by rolls 17 to the exit slot 7.

While the machine may be turned on and off by hand it is preferred to have this done automatically. One means of accomplishing this is to have a whisker switch 21 in a position to touch the copy sheet as it is introduced into the machine via slot 6. Switch 21 is connected to a motor controller and power source 19 in a conventional manner. When the switch 21 senses the sheets it activates the power source which supplies power to motor 18. Another whisker switch 20 is set to engage the original and copy sheet as they exit from the nip formed by roll 17. Upon sensing the passage of the sheets switch 21) operates to turn off the power.

Referring particularly to the improvement of this invention, when the end of an original is at point A in front of the light source on the print roll, the machine must continue to rotate until point A moves approximately to point A on print roll 12 in order to allow the copy and the original to be ejected from the machine. The portion of the transfer sheet that was at point A in front of the light source travels approximately to point B near roller 15. In normal practice this amount of transfer sheet would be wasted, along with that portion of the transfer sheet existing between point A and point C, the point where the next cOpy and original would contact the transfer sheet.

In one embodiment of this invention, when whisker switch 20 senses the passage of the tail end of the sheets is activates a delay switch in power source 19 which causes motor 18 to reverse for a predetermined time before shutting the machine off. A constant speed drive is preferably used. The predetermined time of the reverzsal depends, of course, upon the distance between points C, A and A; but for most machines this will be in the order of 2 to 3 seconds which is sufiicient for the transfer sheet at point B to return back to point A if overlap is to be avoided. The return can be even greater such as for example to return the portion of transfer sheet at point B back to point C which Will'further conserve the amount of copy sheet consumed. If overlap of the originals with respect to the transfer sheet is to be practiced then the amount of return programmed into the machine will be sufficient to carry point B of the transfer sheet to some points in advance of roll 11.

FIG. 2 illustrates one circuit for controlling the drive to be self reversing when a sheet emerges past switch 21). Line voltage is applied across terminals 51 and 52 to energize 3 relays R1, R2 and R3 according to the switching logic shown. Relays R1 and R3 have fast pull in and fast drop out characteristics while relay R2 has a fast pull in and a slow or time delay drop out characteristic. This time delay correspond to the time required for the reverse drive provided by this circuit to accomplish the rewind of the transfer sheet as previously described.

The controls for relay R2 include a normally open switch 21 and a series combination of a normally closed contact RZ-Z and a normally open contact R1-2. It will be understood from the notation used that the contact R2-2 is actuated whenever relay R2 is energized or before it drops out after once being energized due to its time delay drop out characteristic. Similarly the contact R12 will close whenever relay R1 is energized.

Relays R2 and R3 are both energized only during the time when switch 20 is closed.

Motor 18 is energized to be driven whenever contact R2-1 or contact R1-1 is closed. The direction in which motor 18 will rotate is determined by whether or not direction control 53 is energized. When the direction control 53 is energized the motor 13 will run in the direction to drive paper forwardly and when direction control 53 is not energized the motor 18 will run when energized in the reverse direction. Energization of the direction control 53 occurs whenever switch R1-3 or contact R3-1 are closed corresponding to the energized condition for relays R1 and R3 respectively.

The operation of the circuit of FIG. 2 will now be described. When a paper sheet enters slot 6 switch 21 is closed energizing relay R1 to close contact R1-1 to start the motor 18 running and since contact R14) is closed the motor runs in a forward direction. Contact R1-2 also closes to maintain relay R1 energized through the normally closed contact R2-2 in the event that a short piece of paper is fed to the machine which would open switch 21 before the head end of the sheet reached the switch 20.

After the sheet reaches switch 20 and closes, the circuits controlled thereby, relays R2 and R3 are energized and the sealing circuit through R22 is broken. Motor drive circuit completed through contact R2-1. and the motor continues to run in the forward direction by virtue of the closure of contact R3-1. When the tail end of the sheet passes the switch 20 relay R3 drops out immediately and the circuit to direction control 53 is broken, thereby establishing reverse rotation for the motor 18. The motor 18 continues to run in the reverse direction for the interval during which contact R2-1 is closed corresponding to the time delay drop out interval for relay R2.

Another method of accomplishing the reversal of the transfer sheet is to place a spring tensioncd guide roll 22 against the transfer sheet as it leaves supply roll 10. Roller 22 is carried on a pivoted arm 23, the other end of which is attached to a spring 24. When the machine is in forward drive the tension imparted to the roll by takeup roll 16 is sufficient to cause roller 22 to assume the position shown. When the machine is stopped, however, the tension supplied to roll 22 by spring 24 is sufficient to cause the roller to pull the transfer sheet back some distance and for roller 22 to assume the position shown at 22. In this embodiment some means must be incorporated into the machine for reducing or releasing the tension on the transfer sheet. This may be done by equipping roll re between pulley 31 and the main body of the roll with a electromagnetic activated clutch 34 with the clutch being in the open position when the machine is not running. In this embodiment, the circuitry shown in FIGURE 2 is not required. Switch 21 when activated simply turns the machine on, and switch 20 turns it off after the passage of the original and copy. Clutch 34 is connected to the power source 19 and is energized when the machine is on and is de-energized when it is off.

Having described this invention, what is sought to be protected by Letters Patent is succinctly set forth in the following claims.

We claim:

1. In a thermographic copying apparatus having transport means for moving a continuous trans-fer sheet under tension from a supply roll past a printing station to a takeup roll, inlet means for placing a copy sheet and an indicia-bearing original adjacent said transfer sheet at said printing station, a light source adpated to direct high intensity light onto said printing station and cause said copy sheet to be imaged by said transfer sheet according to the pattern on said indicia-bearing original and outlet means adapted to remove said copy sheet and said original after said transfer sheet has advanced with said copy sheet and indicia-bearing original past said printing station, the improvement for decreasing the amount of said transfer sheet consumed per copy comprising reversing means adapted to reverse the movement of said transfer sheet past said printing station during the interval between the removal of said imaged copy sheet and the next printing action, the amount of said reversal being no greater than that required to return said transfer sheet to its original position.

2. The thermographic copying apparatus of claim 1 including a constant speed drive operatively connected to said transport means and adapted to move said transfer sheet past said printing station at a constant speed, said reversing means being operatively associated with said constant speed drive so as to cause reversal thereof, the amount of said reversal being controlled by timing the period said constant speed drive is in reverse.

3. The thermographic copying apparatus of claim 1 wherein said reversing means comprises a spring-loaded backlash roll between said supply roll and said printing station adapted to reverse the motion of said transfer sheet when the tension on said transfer sheet is reduced.

4. The thermographic copying apparatus of claim 1 wherein the amount of said reversal is about equal on the average to the spacing between the trailing edge of one original and the leading edge of the next succeeding original.

References Cited by the Examiner UNITED STATES PATENTS 3,048,695 8/1962 Russell 250-65 X 3,214,585 10/1965 Stroszynski 250-65 RALPH G. NILSON, Primary Examiner. W. F. LINDQUIST, Assistant Examiner. 

1. IN A THERMOGRAPHIC COPYING APPARATUS HAVING TRANSPORT MEANS FOR MOVING A CONTINUOUS TRANSFER SHEET UNDER TENSION FROM A SUPPLY ROLL PAST A PRINTING STATION TO A TAKEUP ROLL, INLET MEANS FOR PLACING A COPY SHEET AND AN INDICIA-BEARING ORIGINAL ADJACENT SAID TRANSFER SHEET AT SAID PRINTING STATION, A LIGHT SOURCE ADAPTED TO DIRECT HIGH INTENSITY LIGHT ONTO SAID PRINTING STATION AND CAUSE SAID COPY SHEET TO BE IMAGED BY SAID TRANSFER SHEET ACCORDING TO THE PATTERN ON SAID INDICIA-BEARING ORIGINAL AND OUTLET MEANS ADAPTED TO REMOVE SAID COPY SHEET AND SAID ORIGINAL AFTER SAID TRANSFER SHEET HAS ADVANCED WITH SAID COPY SHEET 